The effects of two convulsant drugs (penicillin and strychnine) and two anticonvulsants (phenobarbital and diphenylhydantoin) will be studied on synaptic connections between individual axons and neurons in the spinal cord of a primitive vertebrate, the river lamprey. This preparation has the basic organization of higher vertebrate nervous systems while possessing many advantages of invertebrates for experimental neurobiology. These include the ability to study the CNS in isolation, to identify and impale neural elements under the dissecting microscope, and to rapidly alter the extracellular environment. The techniques of intracellular recording and stimulation, statistical analysis of mean quantum content, and intracellular dye injection, will be used to identify monosynaptic connections, and to distinguish among several possible effects on synaptic potency and membrane excitability which might account for the convulsant or anticonvulsant actions of these drugs. This should aid in the search for more effective anticonvulsants by establishing biological assays for possible anticonvulsant actions, and by establishing the lamprey nervous system as a model for such assays.